I could erect you could erect he could erect we could erect you could erect they could erect
V-ing form
I could be erecting you could be erecting he could be erecting we could be erecting you could be erecting they could be erecting
Perfect
I could have erected you could have erected he could have erected we could have erected you could have erected they could have erected
V-ing perfect
I could have been erecting you could have been erecting he could have been erecting we could have been erecting you could have been erecting they could have been erecting
Negation
Simple form
I couldn't erect you couldn't erect he couldn't erect we couldn't erect you couldn't erect they couldn't erect
V-ing form
I couldn't be erecting you couldn't be erecting he couldn't be erecting we couldn't be erecting you couldn't be erecting they couldn't be erecting
Perfect
I couldn't have erected you couldn't have erected he couldn't have erected we couldn't have erected you couldn't have erected they couldn't have erected
V-ing perfect
I couldn't have been erecting you couldn't have been erecting he couldn't have been erecting we couldn't have been erecting you couldn't have been erecting they couldn't have been erecting
Interrogative form
Simple form
could I erect? could you erect? could he erect? could we erect? could you erect? could they erect?
V-ing form
could I be erecting? could you be erecting? could he be erecting? could we be erecting? could you be erecting? could they be erecting?
Perfect
could I have erected? could you have erected? could he have erected? could we have erected? could you have erected? could they have erected?
V-ing perfect
could I have been erecting? could you have been erecting? could he have been erecting? could we have been erecting? could you have been erecting? could they have been erecting?
Interro-negative form
Simple form
couldn't I erect? couldn't you erect? couldn't he erect? couldn't we erect? couldn't you erect? couldn't they erect?
V-ing form
couldn't I be erecting? couldn't you be erecting? couldn't he be erecting? couldn't we be erecting? couldn't you be erecting? couldn't they be erecting?
Perfect
couldn't I have erected? couldn't you have erected? couldn't he have erected? couldn't we have erected? couldn't you have erected? couldn't they have erected?
V-ing perfect
couldn't I have been erecting? couldn't you have been erecting? couldn't he have been erecting? couldn't we have been erecting? couldn't you have been erecting? couldn't they have been erecting?